The transfer bar lift arm to which this invention is directed is used in machining operations where there are a number of stations between which a workpiece is cycled in order to receive different machining operations at each station. The workpiece may be moved by itself, or may be secured to a pallet which is moved. In order to move the workpiece between the stations, the workpiece or pallet rides on transfer bars, and the transfer bars (usually two in side-by-side relation) move forward the prescribed distance between operations. The workpiece or pallet is not fixed to the transfer bars, and when the transfer bars finish their motion, the workpiece or pallet is then set down on some sort of locking and holding mechanism (a fixture) which supports the workpiece for the operation. Before the transfer bar moves, however, it must be raised upwardly (to raise the workpiece prior to transportation), and this is typically accomplished by lift arms of the kind to which this invention is directed. A typical distance through which a transfer bar might be raised by the lift arms is about seven inches.
A patent exemplary of the prior art in this area is U.S. 4,868,960, which issued Sep. 26, 1989 to Takagi et al. This patent shows lift arms controlled by an actuation rod for movement between two extreme positions, one corresponding to the lowest position of the transfer bar, the other corresponding to the highest position of the transfer bar.
Other patents of general interest are the following: U.S. Pat. No. 2,039,754, issued May 5, 1936 to J.B. Tiedemann; U.S. Pat. No. 2,193,840, issued Mar. 19, 1940 to A. Oberhoffken et al; U.S. Pat. No. 2,895,354, issued July 21, 1959 to D.E. Hawkinson et al; U.S. Pat. No. 3,010,371, issued Nov. 28, 1961 to K.A. Riedel et al; U.S. Pat. No. 4,394,897, issued July 26, 1983 to J.H. Brems; U.S. Pat. No. 4,603,456, issued Aug. 5, 1986 to M. Hiroyasu et al; U.S. Pat. No. 4,783,889, Nov. 15, 1988 to S. Hayashi.